Transcript Searches for Permanent Electric Dipole Moments (EDM) of

Searches for
Permanent Electric Dipole Moments (EDM)
of Atoms, Molecules, and the Neutron
Dmitry Budker
University of California, Berkeley
Nuclear Science Division, LBNL
March, 2010
http://budker.berkeley.edu/
The Plan:
• Discrete vs. continuous symmetries
• P, CP, CPT
• EDM and P,T-violation
• How EDM experiments work?
• A brief and incomplete survey
• The LANL neutron EDM experiment
• Kerr Effect in Liquid Helium
What is parity?
z
y
P
x’
x
z’’
y’
z’
Rotation around y’
x’’
y’’=y’
 Left hand cannot be rotated into right hand !
Normal vs. axial vectors
Under Spatial Inversion (P):
• V  -V
r, p, E, d = er, …
•A A
L = rp, S, B
Similarly for scalars (pseudo-scalars)
Under Spatial Inversion (P):
•SS
Energy, any VV’, AA’ …
• PS  -PS
any A V, …
• Continuous:
Discrete vs. Continuous
Transformations and Symmetries
• Translation → momentum conservation
• Translation in time → energy conservation
• Rotation → angular momentum conservation
• Discrete:
• Spatial Inversion (P) → P-invariance (parity)
• Charge Conjugation (C) → C-invariance
• Time reversal (T) → T-invariance
• CP
• CPT
• Permutation of identical particles → PSP, spin-statistics
The (broken) law of parity
 Because the laws of Nature should be the same in
the “real” world and its mirror image, no pseudoscalar correlation should be observed in
experiments, for example
 
Ip
 Does not apply to cork-screws !
The theorists who said: check it !
Prof. C. N. Yang
Prof. T. D. Lee
Prof. C. S. Wu (1913-1997)
The shatterer of the
parity illusion (1956)…
The Co-60 experiment
CP, CPT, P and T
• Symmetry is restored by CP (L.D. Landau, and others)
• CP-violation discovered in 1964 (Cronin, Fitch, et. al.)
• Important for matter-anti-matter asymmetry
• Only K-mesons, and since very recently, also B-mesons
• CPT is still good (for now)
Prof. James Cronin lecturing on CP-violation in Kaon decays
Novosibirsk, USSR, September 1986
CPT theorem: a “proof”
• For an even-dimensional space, P=rotation
y
y
P
Rotation
x
x
Prof. Iosif B. Khriplovich
x
y
• Our space-time has 4 dimensions → try PT
P
T
jμ = (ρ,j) → (ρ,-j) → (ρ,j)
• Time component is associated with energy → to flip sign, try C
CPT
jμ = (ρ,j) → (-ρ,-j)
☺
Permanent EDM of a particle
contradicts both
P- and T-invariance
d
T
J
P
EDMs of various particles (e·cm)
Experimental Standard
reach (???) Model (SM)
10-28
10-34-10-31
n
Present upper
limit on |d|
(6-10) ·10-26
e
1.6 ·10-27
10-30
10-40-10-38
μ
10-18
4 ·10-24
10-24
10-25
10-38
10-34-10-31
3.1 ·10-29
10-29
p (from
199Hg)
199Hg
Beyond SM
SUSY
Left-Right Symmetric
SO(10) GUT
…
EDM experiments have killed MOST models of CP-violation in Kaons !
EDM causes spin to precess in
an electric field
z
E
y
x
Universal Statistical Sensitivity
Formula
 2 1
1
d 
 
4 E NT
Electric field
Number of Particles
Coherence Time
Lifetime of Experimentalist
EDM of the Electron
• Heavy atoms and molecules amplify the EDM
(dat/ de~ Z3α2 P.G.H. Sandars, Oxford, 1960s)
• Best current limit |de|<1.5·10-27 e·cm from
E.D. Commins et al (1985-2001), Tl
• A challenge is set !
Professor Eugene D. Commins
ComminsFest Symposium
May 20-21, 2001, Berkeley
ComminsFest
Book
Atomic EDMs measured in
Rb
Cs
Fe3+
205Tl
129Xe 3P
2
129Xe 1S
0
199Hg
J
1/2
1/2
3/2
I
3/2,5/2
7/2
0
1/2
2
0
1/2
1/2
1/2
0
1/2
Also proposed/considered/pursued: you name it !
Molecular EDMs
measured in
TlF
YbF
Ra, Rn, Dy, Sm, Yb, Ba, Au, Fr, Gd3+
Also proposed/considered/pursued:
LuO, CsF, PbF, PbI, BiO, BiS, YbH,
VdV molecules, e.g., CsXe,
PbO*
Neutron EDM: the time line
?
Prof. N. F. Ramsey
Retires
Prof. Norman F. Ramsey
“What if we see an EDM?”
Ultra-Cold Neutrons (UCN)
•Proposal: Ya. B. Zel'dovich, Sov. Phys. JETP, 9, 1389 (1959)
•First realizations: 1969, Dubna and Garching
•Problem with production -- tiny fraction in Maxwellian distribution (~10-11 at T=30 K)
Materials used for UCN storage:
The ILL
UCN
Source
The ILL n-EDM Experiment
 2 1
1
d 
 
4 E NT
• Ramsey separated-field method
• N = 13,000; n~1/cm3
• Storage time:  = 130 s
• E = 4.5 kV/cm
• 199Hg co-magnetometer
• Statistics-limited
The LANSCE/SNS n-EDM experiment
Features :
 Create UCN in place in
4He
 3He comagnetometer
 HV for E field generated
internally
 SQUIDs to detect 3He
spin precession
 3He capture/4He
scintillation detection
UCN Source
Neutron EDM experiment at LANSCE
Light Guides
Cells Between
Electrodes
HV and Ground
Electrodes
Beam Entrance
Window
Cosq Coil
SQUID Enclosure
HV Variable Capacitor
Polarized 3He Source
Justin Torgerson
Steve Lamoreaux
3He
as Analyzer
Concept for HV generator
500 kV
50 kV
Variable capacitor in LHe volume
Accurate E-reversal, stability and
field-monitoring are essential!
The Ev systematics:
Ev / c 
2
 
L
~5·10-8
Hz
for both n
and 3He

2
c
2
c~L/v
Motional
magnetic field
 B
0
~3 Hz
S. K. Lamoreaux, PRA 53(6), R3705, 1996
D. Budker, D. F. Kimball, and D. P. DeMille, “Atomic physics:
Exploration in Problems and Solutions,” Oxford, 2003
E-field requirements
• Homogeneity over cell volume
• Stability over 500 s
• Reversibility
<1%
This reduces E-field-related systematics to < 510-10 Hz,
i.e. one tenth of the EDM shift for dn=10-28 e cm
Electric field monitoring ~ 0.1% -1%
The Kerr Effect
• Uniaxial E-field-induced anisotropy:
n = n||-n=
2
KE0
• For input light polarized at 45o to E, the induced
ellipticity:   Ln /   L /  KE02
• Circular analyzer
I1  I 2

I1  I 2
• Achievable sensitivity:   10
-8
rad Hz-1/2
Electric Field Measurement
Kerr constant for LHe estimated from experimental data for
-20
2
He at 300K:
K ≈ 1.7·10 (cm/V)
Electric field:
E0 = 50 kV/cm
Sample length:
L = 10 cm
 ≈ 10 rad
-1/2
-8
A 1s measurement gives accuracy ( ≈ 10 rad Hz ):
-5
Induced ellipticity:
E0/E0 ≈ 5·10
-4
? Kerr constant for superfluid He ?
Cryostat (T 1.4 K)
with optical access
Test set-up at Berkeley
Laser
Thin-wall
st. steel tube
Home-made
cryogenic
HV cable
Copper
electrodes
l=38 mm
gap=6 mm
Graduate student
A. Sushkov
Electrode
Assembly
HV cableconnector
Results: LN2 Kerr constant
Measurement:
K = 4.2(1)·10-18 (cm/V)2
Literature result:
K = 4.0·10-18 (cm/V)2
K.Imai et. al., Proceedings of the 3rd
Int. Conf. On Prop. and App. Of Diel.
Mat., 1991 Japan)
E max = 60 kV/cm
Eric Williams
LHe Kerr Constant Measurements
Martin Cooper
A. Sushkov, Val Yashchuk, S. Lamoreaux
Results: LHe Kerr constant (T≈1.4 K)
Measurement:
K = 2.45(13)·10-20 (cm/V)2
Theoretical value:
(1s, 2s, 2p levels)
K = 2.0·10-20 (cm/V)2
 Temperature
dependence!
E max = 50 kV/cm
Summary
• EDM experiments are among the most sensitive probes of Physics
Beyond the Standard Model
• Steady progress in atoms and molecules
• Progress with n-EDM has slowed down in 1990s, but radically new
experiments are in preparation; optimistic prospects (if funded)
• Kerr effect in He for the LANL experiment
• Only a few experiments were mentioned in this talk; vast literature
available (e.g., book by Khriplovich&Lamoreaux)
And our book
•EDM-related colloquia (recorded):
D. DeMille
PbO* (e-EDM)
w/ Kimball &
DeMille !
M. Romalis
Hg, LXe (a radically new approach)